土木工程畢業(yè)設(shè)計外文翻譯最終中英文

7Rigid-FrameStructuresArigid-framehigh-risestructuretypicallycomprisesparallelororthogonallyarrangedbentsconsistingofcolumnsandgirderswithmomentresistantjoints.Resistancetohorizontalloadingisprovidedbythebendingresistanceofthecolumns,girders,andjoints.Thecontinuityoftheframealsocontributestoresistinggravityloading,byreducingthemomentsinthegirders.Theadvantagesofarigidframearethesimplicityandconvenienceofitsrectangularform.Itsunobstructedarrangement,clearofbracingmembersandstructuralwalls,allowsfreedominternallyforthelayoutandexternallyforthefenestration.Rigidframesareconsideredeconomicalforbuildingsofupto'about25stories,abovewhichtheirdriftresistanceiscostlytocontrol.If,however,arigidframeiscombinedwithshearwallsorcores,theresultingstructureisverymuchstiffersothatitsheightpotentialmayextendupto50storiesormore.Aflatplatestructureisverysimilartoarigidframe,butwithslabsreplacingthegirdersAswitharigidframe,horizontalandverticalloadingsareresistedinaflatplatestructurebytheflexuralcontinuitybetweentheverticalandhorizontalcomponents.Ashighlyredundantstructures,rigidframesaredesignedinitiallyonthebasisofapproximateanalyses,afterwhichmorerigorousanalysesandcheckscanbemade.Theproceduremaytypicallyincludethefollowingstages:1.Estimationofgravityloadforcesingirdersandcolumnsbyapproximatemethod. 2.Preliminaryestimateofmembersizesbasedongravityloadforceswitharbitraryincreaseinsizestoallowforhorizontalloading.3.Approximateallocationofhorizontalloadingtobentsandpreliminaryanalysisofmemberforcesinbents.4.Checkondriftandadjustmentofmembersizesifnecessary.5.Checkonstrengthofmembersforworstcombinationofgravityandhorizontalloading,andadjustmentofmembersizesifnecessary.6.Computeranalysisoftotalstructureformoreaccuratecheckonmemberstrengthsanddrift,withfurtheradjustmentofsizeswhererequired.Thisstagemayincludethesecond-orderP-Deltaeffectsofgravityloadingonthememberforcesanddrift..7.Detaileddesignofmembersandconnections.Thischapterconsidersmethodsofanalysisforthedeflectionsandforcesforbothgravityandhorizontalloading.Themethodsareincludedinroughlytheorderofthedesignprocedure,withapproximatemethodsinitiallyandcomputertechniqueslater.StabilityanalysesofrigidframesarediscussedinChapter16.7.1RIGIDFRAMEBEHAVIORThehorizontalstiffnessofarigidframeisgovernedmainlybythebendingresistanceofthegirders,thecolumns,andtheirconnections,and,inatallframe,bytheaxialrigidityofthecolumns.Theaccumulatedhorizontalshearaboveanystoryofarigidframeisresistedbyshearinthecolumnsofthatstory<Fig.7.1>.Theshearcausesthestory-heightcolumnstobendindoublecurvaturewithpointsofcontraflexureatapproximatelymid-story-heightlevels.Themomentsappliedtoajointfromthecolumnsaboveandbelowareresistedbytheattachedgirders,whichalsobendindoublecurvature,withpointsofcontraflexureatapproximatelymid-span.Thesedeformationsofthecolumnsandgirdersallowrackingoftheframeandhorizontaldeflectionineachstory.Theoveralldeflectedshapeofarigidframestructureduetorackinghasashearconfigurationwithconcavityupwind,amaximuminclinationnearthebase,andaminimuminclinationatthetop,asshowninFig.7.1.Theoverallmomentoftheexternalhorizontalloadisresistedineachstorylevelbythecoupleresultingfromtheaxialtensileandcompressiveforcesinthecolumnsonoppositesidesofthestructure<Fig.7.2>.Theextensionandshorteningofthecolumnscauseoverallbendingandassociatedhorizontaldisplacementsofthestructure.Becauseofthecumulativerotationuptheheight,thestorydriftduetooverallbendingincreaseswithheight,whilethatduetorackingtendstodecrease.Consequentlythecontributiontostorydriftfromoverallbendingmay,in.theuppermoststories,exceedthatfromracking.Thecontributionofoverallbendingtothetotaldrift,however,willusuallynotexceed10%ofthatofracking,exceptinverytall,slender,,rigidframes.Thereforetheoveralldeflectedshapeofahigh-riserigidframeusuallyhasashearconfiguration.Theresponseofarigidframetogravityloadingdiffersfromasimplyconnectedframeinthecontinuousbehaviorofthegirders.Negativemomentsareinducedadjacenttothecolumns,andpositivemomentsofusuallylessermagnitudeoccurinthemid-spanregions.Thecontinuityalsocausesthemaximumgirdermomentstobesensitivetothepatternofliveloading.Thismustbeconsideredwhenestimatingtheworstmomentconditions.Forexample,thegravityloadmaximumhoggingmomentadjacenttoanedgecolumnoccurswhenliveloadactsonlyontheedgespanandalternateotherspans,asforAinFig.7.3a.Themaximumhoggingmomentsadjacenttoaninteriorcolumnarecaused,however,whenliveloadactsonlyonthespansadjacenttothecolumn,asforBinFig.7.3b.Themaximummid-spansaggingmomentoccurswhenliveloadactsonthespanunderconsideration,andalternateotherspans,asforspansABandCDinFig.7.3a.Thedependenceofarigidframeonthemomentcapacityofthecolumnsforresistinghorizontalloadingusuallycausesthecolumnsofarigidframetobelargerthanthoseofthecorrespondingfullybracedsimplyconnectedframe.Ontheotherhand,whilegirdersinbracedframesaredesignedfortheirmid-spansaggingmoment,girdersinrigidframesaredesignedfortheend-of-spanresultanthoggingmoments,whichmaybeoflesservalue.Consequently,girdersinarigidframemaybesmallerthaninthecorrespondingbracedframe.Suchreductionsinsizealloweconomythroughthelowercostofthegirdersandpossiblereductionsinstoryheights.Thesebenefitsmaybeoffset,however,bythehighercostofthemorecomplexrigidconnections.7.2APPROXIMATEDETERMINATIONOFMEMBERFORCESCAUSEDBYGRAVITYLOADSIMGArigidframeisahighlyredundantstructure;consequently,anaccurateanalysiscanbemadeonlyafterthemembersizesareassigned.Initially,therefore,membersizesaredecidedonthebasisofapproximateforcesestimatedeitherbyconservativeformulasorbysimplifiedmethodsofanalysisthatareindependentofmemberproperties.Twoapproachesforestimatinggirderforcesduetogravityloadingaregivenhere.7.2.1GirderForces—CodeRecommendedValuesInrigidframeswithtwoormorespansinwhichthelongerofanytwoadjacentspansdoesnotexceedtheshorterbymorethan20%,andwheretheuniformlydistributeddesignliveloaddoesnotexceedthreetimesthedeadload,thegirdermomentandshearsmaybeestimatedfromTable7.1.ThissummarizestherecommendationsgivenintheUniformBuildingCode[7.1].Inothercasesaconventionalmomentdistributionortwo-cyclemomentdistributionanalysisshouldbemadeforalineofgirdersatafloorlevel.7.2.2Two-CycleMomentDistribution[7.2].Thisisaconciseformofmomentdistributionforestimatinggirdermomentsinacontinuousmultibayspan.ItismoreaccuratethantheformulasinTable7.1,especiallyforcasesofunequalspansandunequalloadingindifferentspans.Thefollowingisassumedfortheanalysis:1.Acounterclockwiserestrainingmomentontheendofagirderispositiveandaclockwisemomentisnegative.2.Theendsofthecolumnsatthefloorsaboveandbelowtheconsideredgirderarefixed.3.Intheabsenceofknownmembersizes,distributionfactorsateachjointaretakenequalto1/n,wherenisthenumberofmembersframingintothejointintheplaneoftheframe.Two-CycleMomentDistribution—WorkedExample.Themethodisdemonstratedbyaworkedexample.InFig,7.4,afour-spangirderAEfromarigid-framebentisshownwithitsloading.Thefixed-endmomentsineachspanarecalculatedfordeadloadingandtotalloadingusingtheformulasgiveninFig,7.5.ThemomentsaresummarizedinTable7.2.Thepurposeofthemomentdistributionistoestimateforeachsupportthemaximumgirdermomentsthatcanoccurasaresultofdeadloadingandpatternliveloading.Adifferentloadcombinationmustbeconsideredforthemaximummomentateachsupport,andadistributionmadeforeachcombination.ThefivedistributionsarepresentedseparatelyinTable7.3,andinacombinedforminTable7.4.DistributionsainTable7.3arefortheexteriorsupportsAandE.ForthemaximumhoggingmomentatA,totalloadingisappliedtospanABwithdeadloadingonlyonBC.Thefixed-endmomentsarewritteninrows1and2.Inthisdistributiononly.theresultingmomentatAisofinterest.Forthefirstcycle,jointBisbalancedwithacorrectingmomentof-<-867+315>/4=-U/4assignedtoMBAwhereUistheunbalancedmoment.Thisisnotrecorded,buthalfofit,<-U/4>/2,iscarriedovertoMAB.Thisisrecordedinrow3andthenaddedtothefixed-endmomentandtheresultrecordedinrow4.ThesecondcycleinvolvesthereleaseandbalanceofjointA.Theunbalancedmomentof936isbalancedbyadding-U/3=-936/3=-312toMBA<row5>,implicitlyaddingthesamemomenttothetwocolumnendsatA.Thiscompletesthesecondcycleofthedistribution.TheresultingmaximummomentatAisthengivenbytheadditionofrows4and5,936-312=624.ThedistributionforthemaximummomentatEfollowsasimilarprocedure.DistributionbinTable7.3isforthemaximummomentatB.ThemostsevereloadingpatternforthisiswithtotalloadingonspansABandBCanddeadloadonlyonCD.TheoperationsaresimilartothoseinDistributiona,exceptthattheTfirstcycleinvolvesbalancingthetwoadjacentjointsAandCwhilerecordingonlytheircarryovermomentstoB.Inthesecondcycle,Bisbalancedbyadding-<-1012+782>/4=58toeachsideofB.Theadditionofrows4and5thengivesthemaximumhoggingmomentsatB.Distributionscandd,forthemomentsatjointsCandD,followpatternssimilartoDistributionb.ThecompletesetofoperationscanbecombinedasinTable7.4byinitiallyrecordingateachjointthefixed-endmomentsforbothdeadandtotalloading.Thenthejoint,orjoints,adjacenttotheoneunderconsiderationarebalancedfortheappropriatecombinationofloading,andcarryovermomentsassigned.totheconsideredjointandrecorded.Thejointisthenbalancedtocompletethedistributionforthatsupport.MaximumMid-SpanMoments.Themostsevereloadingconditionforamaximummid-spansaggingmomentiswhentheconsideredspanandalternateotherspansandtotalloading.Aconcisemethodofobtainingthesevaluesmaybeincludedinthecombinedtwo-cycledistribution,asshowninTable7.5.Adoptingtheconventionthatsaggingmomentsatmid-spanarepositive,amid-spantotal;loadingmomentiscalculatedforthefixed-endconditionofeachspanandenteredinthemid-spancolumnofrow2.Thesemid-spanmomentsmustnowbecorrectedtoallowforrotationofthejoints.Thisisachievedbymultiplyingthecarryovermoment,row3,attheleft-handendofthespanby<1+0.5D.F.>/2,andthecarryovermomentattheright-handendby-<1+0.5D.F.>/2,whereD.F.istheappropriatedistributionfactor,andrecordingtheresultsinthemiddlecolumn.Forexample,thecarryovertothemid-spanofABfromA=[<1+0.5/3>/2]x69=40andfromB=-[<1+0.5/4>/2]x<-145>=82.Thesecorrectionmomentsarethenaddedtothefixed-endmid-spanmomenttogivethemaximummid-spansaggingmoment,thatis,733+40+82=8ColumnForcesThegravityloadaxialforceinacolumnisestimatedfromtheaccumulatedtributarydeadandlivefloorloadingabovethatlevel,withreductionsinliveloadingaspermittedbythelocalCodeofPractice.Thegravityloadmaximumcolumnmomentisestimatedbytakingthemaximumdifferenceoftheendmomentsintheconnectedgirdersandallocatingitequallybetweenthecolumnendsjustaboveandbelowthejoint.Tothisshouldbeaddedanyunbalancedmomentduetoeccentricityofthegirderconnectionsfromthecentroidofthecolumn,alsoallocatedequallybetweenthecolumnendsaboveandbelowthejoint.第七章框架結(jié)構(gòu)高層框架結(jié)構(gòu)一般由平行或正交布置的梁柱結(jié)構(gòu)組成,梁柱結(jié)構(gòu)是由帶有能承擔彎矩作用節(jié)點的梁、柱組成。具有抗彎能力的梁、柱和節(jié)點共同作用抵抗水平荷載。連續(xù)框架可降低梁的跨中彎矩而有利于抵抗重力荷載?？蚣芙Y(jié)構(gòu)有簡捷和便于采用矩形體系的優(yōu)點。由于這種布置形式?jīng)]有斜支撐和結(jié)構(gòu)墻體,因此,沒有不便利之處,部可以自由布置,外部可以自由設(shè)計門、窗?？蚣芙Y(jié)構(gòu)對于25層以的建筑是經(jīng)濟的,超過25層由于要限制其位移而花費的代價高,顯得很不經(jīng)濟。如果框架與剪力墻及芯筒相結(jié)合,剛度能夠大幅度提高,可以建造50層以上的建筑。板柱結(jié)構(gòu)與框架結(jié)構(gòu)非常相似,不同之處僅是用板代替了梁。和框架結(jié)構(gòu)一樣,板柱結(jié)構(gòu)是通過其水平和豎向構(gòu)件之間的連續(xù)抗彎作用來抵抗水平和豎向荷載。對于高次超靜定框架結(jié)構(gòu),應(yīng)根據(jù)近似分析進行初步設(shè)計,隨后進行精確分析和校核。分析過程一般包括以下幾步:1．按近似方法確定梁和柱所受重力荷載;2．初步確定在重力荷載作用下構(gòu)件的截面尺寸,考慮水平荷載的作用進行構(gòu)件截面尺寸的任意調(diào)整;3．將水平荷載分配到各梁柱結(jié)構(gòu)上,對這些結(jié)構(gòu)構(gòu)件的力進行初步分析;4．檢驗位移并對構(gòu)件截面尺寸做必要的調(diào)整;5．按最不利的重力荷載和水平荷載組合檢驗構(gòu)件強度,做必要的構(gòu)件截面尺寸調(diào)整;6．為了更精確地驗算構(gòu)件強度和位移,利用計算機對結(jié)構(gòu)進行整體分析,需要時則近一步調(diào)整構(gòu)件截面尺寸。這一階段中應(yīng)包括考慮重力荷載對構(gòu)件力和位移產(chǎn)生的Ρ一△二階效應(yīng);7．構(gòu)件和節(jié)點的詳細設(shè)計。本章討論在重力和水平荷載作用下結(jié)構(gòu)的變形和力分析方法。這些方法基本上按照設(shè)計過程中的次序介紹,首先是近似法,然后介紹計算機分析技術(shù)?？蚣芙Y(jié)構(gòu)的穩(wěn)定性分析將在第十六章中討論。7.1框架結(jié)構(gòu)的性能框架結(jié)構(gòu)的側(cè)向剛度主要取決于梁、柱及節(jié)點的抗彎能力,在較高的框架中主要取決于柱子的軸向剛度。作用于框架任一層間的水平集中剪力由該層柱子的抗剪能力抵抗<圖7.1>。剪力使框架結(jié)構(gòu)每層的柱產(chǎn)生雙曲率彎曲,其反彎點大約在層高的中間部位。上、下柱引起的作用于節(jié)點處的彎矩由相鄰梁承擔,該梁、柱的變形引起框架的整體變形,使各層間產(chǎn)生水平位移。在水平推力作用下結(jié)構(gòu)的整體變形和剪力圖如圖7.1所示,其凹面朝向風荷載作用方向,最大傾角在基底附近,最小傾角在頂端。外部水平荷載產(chǎn)生的總彎矩由各層間兩個邊柱中的軸向拉、壓力組成的力矩抵抗<圖7.2>。柱子的伸、縮引起結(jié)構(gòu)的整體彎曲變形,并產(chǎn)生相應(yīng)的水平位移。因為轉(zhuǎn)角沿建筑高度累加,所以整體彎曲變形引起的層間位移隨高度增加而增加,而剪切變形引起的層間位移隨高度的增加而減小。其結(jié)果在建筑的最頂部整體彎曲對層間位移的貢獻會大大超過剪切變形對層間位移的貢獻。但是,整體彎曲變形對總位移的貢獻與剪切變形對總位移的貢獻之比不會超過10％,除非在極高或細長的框架中。因此,高層框架結(jié)構(gòu)變形型式為剪切型。從梁的連接受力性能來看,高層建筑采用的剛性節(jié)點連續(xù)的框架不同于一般簡單連接的普通框架。梁在柱邊附近產(chǎn)生負彎矩,跨中正彎矩值常常很小。這種連續(xù)性能使梁中最大彎矩對活荷載的作用方式非常敏感。如果能夠估計出產(chǎn)生最不利彎矩的因素,則必須加以認真的考慮。例如,重力荷載作用下梁在邊柱附近產(chǎn)生的最大負彎矩只會在活荷載作用于邊跨和相間跨時才能發(fā)生,如圖7.3a中的A點。而梁在柱附近產(chǎn)生的最大負彎矩只會在活荷載作用于相鄰跨時才能發(fā)生,如圖7.3a中的B點。當活荷載作用于本跨和相間跨時,梁的跨中正彎矩最大,如圖7.3a中的AB和CD跨?？蚣艿某叽缛Q于柱子在水平荷載作用·下的抗彎強度,這往往會使框架柱的截面尺寸大于相應(yīng)全對角支撐簡單連接框架的柱截面尺寸。另外,框架支撐結(jié)構(gòu)中的梁被設(shè)計為只具有跨中正彎矩,而框架結(jié)構(gòu)的梁則被設(shè)計為端部為負彎矩和跨中為正彎矩,跨中彎矩值較小。因此,框架結(jié)構(gòu)中梁的截面尺寸會小于相應(yīng)的框架支撐結(jié)構(gòu)中梁的截面尺寸。梁截面的減小將會降低其造價,有時可以降低層高,經(jīng)濟效益明顯。但是,由于剛性節(jié)點的處理相當復(fù)雜,代價較高,使上述經(jīng)濟優(yōu)勢被削弱。7.2重力荷載作用下構(gòu)件力的近似計算框架結(jié)構(gòu)是多次超靜定結(jié)構(gòu),因此,只有在確定了構(gòu)件截面尺寸后才能進行精確分析。所以,在初步設(shè)計階段,可根據(jù)傳統(tǒng)的公式和不考慮構(gòu)件特征值的簡化分析法近似確定構(gòu)件中的力,以此為基礎(chǔ)確定構(gòu)件的截面尺寸。下面將討論在重力荷載作用下構(gòu)件力計算的兩種方法。7.2.1梁的力—規(guī)推薦值對于兩跨以上的框架結(jié)構(gòu),當任何相鄰兩跨中的長跨不超過短跨的20%跨度,同時設(shè)計均布活荷載不超過3倍的恒載時,梁的彎矩和剪力可以按表7.1確定。表中各數(shù)值是根據(jù)統(tǒng)筑規(guī)[7.1]中的推薦值給出。對于其它情況,可按照樓面連續(xù)梁采月傳統(tǒng)彎矩分配法或兩次循環(huán)彎矩分配法進行分析確定。7.2.2彎